Telecommunication systems embodying automatic exchanges



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ATTORNEY May 22, 1956 A. A. cHuBB ETAL TELECOMMUNICATION SYSTEMS EMBODYING AUTOMATIC EXCHANGES 19 Sheets-Sheet 19 Filed Sept. 18. 1951 ATTORNEY United States Patent TELECOMMUNICATON SYSTEMS EMBDYING AUTOMATC EXCHANGES Alexander Albert Chubb, Coventry, England, and Maurice Moise Levy, ttawa, Ontario, Canada, assignors to The General Electric Company Limited, London, England Application September 18, 1951, Serial No. 247,072

Claims priority, application Great Britain September 21, 1950 9 Claims. (Cl. 179-13) The present invention relates to telecommunication systems embodying automatic exchanges. Such systems are commonly used in telephony but may be used in other elds such as for example, telegraphy and remote metering.

In automatic exchange practice it is usual to employ automatic switching apparatus which performs the dual function of routing a calling signal from a calling subscriber to the called subscriber and subsequently providing the link through which conversation takes place.

A disadvantage of this arrangement arises from the fact that as the same automatic switching apparatus is used for providing the link through which conversations take place, as well as for calling the called subscribers, the major factors determining the quantity of automatic switching apparatus required at an exchange are the number of subscribers, the average number of calls in a given period (the calling rate) and the average duration of conversations. The average time taken -to establish a call is a minor factor.

One object of the present invention is to provide an improved automatic exchange in which the average duration of conversation is a minor factor in determining the quantity of automatic switching apparatus required.

According to the present invention an automatic exchange comprises a plurality of communication channels, line terminating apparatus responsive to an initial calling signal from a calling station to select a free one of said channels, routing apparatus adapted, in response to dialling signals from the calling station to route to the line terminating apparatus of the called station an identification signal identifying the selected one of the channels, and further apparatus responsive to the channel identification signal to connect the called station to the selected channel.

Other objects and features of the invention will be ap- 'P parent from the following description of the invention given, by way of example, with reference to the accompanying drawings in which:

Figure l is a block diagram of an automatic telephone exchange according to the invention,

Figuresl 2 to l2 are circuit diagrams of parts shown in block form in Figure l,

Figure 13 is an explanatory diagram,

Figure l-'l is a circuit diagram of a part shown in block form in Figure l,

Figures l5 and 16 are explanatory diagrams,

Figures 17 and 18 are circuit diagrams showing modifications of the arrangements of Figures 3 and 5 respectively, and

Figure 19 is a schematic diagram illustrating the manner in which the circuit diagrams of Figures 2 to 12 and 14 are interconnected to form the block diagram of Figure 1.

Referring to Figure 1, this is a block schematic diagram of an automatic telephone exchange for use with 2,000 subscribers. Of the 2,000 subscribers stations connected to the exchange, one is shown at and another ice at 11, the station 10 'being terminated in the exchange at subs line circuit I12 and the station 11 being terminated in the exchange at subs line circuit 13, to be described later.

The exchange contains communication channels provided by a 100 channel, time-sharing pulse communication arrangement. This arrangement comprises a pulse generator 14 adapted to generate pulses suitable for combination to provide the 100 channels at a pulse repetition frequency of 8,000 P. P. S. as will be described later. The 100 channels are terminated at one end by 100 calling units respectively of which one is shown at 1S. 100 called units are provided for terminating the `other ends of the 100 channels respectively when in use, one of the called units bein-g shown at 16. The calling and called units will be described later. Signals between the calling and called units pass through a Go speech junction 17, a Return speech junction 18, or a metering and release junction 19 `as the case may be. In the event of a called subscriber being engaged, a busy signal is transmitted to the calling subscriber by Wayl of a busy junction 20 as will be described later.

In addition to the pulse generator 14 a pulse generator 21 is provided for the purpose of generating pulses suitable for use in routing a callin-g signal to the terminal equipment 13 of a called subscriber. For the purpose of routing the calling signal to the terminal equipment of the called subscriber a router 22 (to be described later) is employed. Th-e router is operated under the control of a register contained in block 23 in Figure 1.

Assuming the subscriber at station 10 to ybe calling the subscriber at station 11 the tirst operation occurs in the subs line circuit 12. This contains a linder which linds a free calling unit. An allotter 24 (to be described later) then comes into operation and allots a free register and calling unit finder 23 to the calling unit. The calling unit finder operates to connect the calling unit 15 found by rthe subs line circuit 12 to the allotted register 23. A dialling tone is then automatically transmitted to the calling subscriber.

Dialling impulses from the calling subscribers station are transmitted to the register where they are stored on four uniselectors (not shown in :Figure l). Pulses are applied from the pulse generator 21 to the uniselectors which serve to :select pulses representative of the four digits dialled. These selected pulses are transmitted, together with pulses representative of the channel number of the free calling unit yfound by the subs line circuit 12, to the router 22. The router transmits to the line circuit 13 of -the called subscriber 11 a pulse representative of the last digit in the number dialled and the pulses representative of the channelv number of the seized calling unit 15.

The line circuit 13, on reception of these pulses, lindsv a free called unit 16. When the free called unit is seized the pulses representative of the channel number of the seized calling unit are transmitted to a translator 25. The translator contains uni-selectors to be described later which are set to positions dependent upon the charac- -teristies of the received pulses and apply the appropriate speech channel pulses to the called unit from the pulse generator 14 to enable communication to be established between the seized calling and called units, through the Go and Return speech junctions 17 and 18. A ringing tone is then automatically transmitted to the called subscribers station. Signals for controlling the metering of the call and for releasing the register 23 and router 22 are transmitted through the metering and release junction 19. i

The automatic exchange shown in Figure 1 will now be subscribed in more detail with reference to Figures 2 to 15 and 19. Throughout Figures 2 to 15 all relays and 

